Optical pickup device and method to read from and record information to disks of different thicknesses

ABSTRACT

An optical pickup device which is efficient in light use having little spherical aberration. The optical pickup device of an optical pickup includes an objective lens, disposed opposite a disk, having a light passing region divided into central, intermediate and periphery regions corresponding to a near axis area, an intermediate axis area and a far axis area of incident light, where the curvature of the central and peripheral regions is optimized for a thin disk and that of the intermediate region is optimized for a thick disk; a light source irradiating light toward a disk through the objective lens; a photo detector for detecting light reflected from the disk; and a beam splitter, disposed between the objective lens and the light source, for transmitting light from the light source toward the objective lens and for diffracting light reflected from the disks toward the photo detector. Therefore, the optical pickup device can be used for both compact disks (CDs) that are thick using light beam passing the near and intermediate regions of said objective lens, and digital video disks (DVDs) that are thin using light beam passing the near and far axis regions of said objective lens, and detect signals without picking up noise regardless of the thickness of the disk.

This application is a continuation of application Ser. No. 08/779,521,filed Jan. 7, 1997, now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an optical pickup device which isapplied to an optical pickup apparatus and method therefor, and moreparticularly, to an optical pickup device and method which enablesreading out of information from optical disks having differentthicknesses and enables recording information thereon.

In the optical pickup, an objective lens faces a recording surface of anoptical disk for focusing light to record information onto the recordingsurface of the disk or receiving light reflected from the surface of thedisk to read information.

2. Description of the Related Art

Recently, research on an optical drive has been conducted in which thedrive can seat disks having different thicknesses by adopting a lensdevice including both a hologram lens and a refractive lens.

FIGS. 1 and 2 show focusing states of a conventional optical pickupdevice of light incident by zero order diffracted light and 1st orderdiffracted light on a thin disk and a thick disk, respectively. Arefractive lens 2 and a hologram lens 1 are disposed in sequence alongan optical path from each of disks 3a and 3b. The hologram lens 1 has alattice pattern 11 for diffracting light that passes through thehologram lens 1. Thus, while light 4 emitted from a light source (notshown) passes through the hologram lens 1, light is divided into adiffracted 1st order light 41 and a non-diffracted zero order light 40,respectively. While the diffracted 1st order light 41 and the nondiffracted zero order light 40 pass through each of the objective lenses2, the light 41 and 40 are focused with different intensities, therebyforming a focus on the thin disk 3a and on the thick disk 3b.

The lens device described above can record information on disks havingdifferent thicknesses and read out information therefrom using zeroorder light and 1st order light. However, as the incident light isdivided into zero order light and 1st order light, the efficiency oflight use is lowered. That is, since the incident light is divided intozero order light and 1st order light by the hologram lens 1, the actualamount of light used for recording information is only 15%. Also, wheninformation is reproduced, information is included in only one of zeroorder light and 1st order light. Thus, 1st order light or zero orderlight without information is detected by a photo detector and thedetected light may produce noise. The above problem can be overcome byprocessing the hologram lens of the lens device. However, this requiresa high precision process of etching a fine pattern on the hologram,thereby increasing the manufacturing cost.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an optical pickupdevice wherein parts thereof can be manufactured and assembled easily atlow cost.

It is another object of the present invention to provide an opticalpickup device which has high efficiency of light use and low sphericalaberration.

To achieve the above and other objects, there is provided an opticaldevice comprising a light source; an objective lens facing a disk havinga light passing region divided into central, intermediate and peripheryregions respectively corresponding to a near axis area, an intermediateaxis area and a far axis area of incident light, wherein the curvatureof the central and peripheral regions are optimized for a thin disk andthat of the intermediate region is optimized for a thick disk; a photodetector for detecting light reflected from the disk; a beam splitter,disposed between the objective lens and the light source, fortransmitting/reflecting light from the light source toward the objectivelens and for reflecting/transmitting light reflected from the diskstoward the photo detector.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects and advantages of the present invention willbecome more apparent by describing in detail a preferred embodimentthereof with reference to the attached drawings in which:

FIG. 1 is a schematic diagram of a conventional lens device having ahologram lens focusing on a thin disk;

FIG. 2 is a schematic diagram of the lens device of FIG. 1 focusing on athick disk;

FIG. 3 is a schematic diagram of an optical pickup device according tothe present invention;

FIGS. 4 and 5 are perspective and front views of an objective lensadopted into the optical pickup device according to the presentinvention;

FIG. 6 is a diagram showing an optical path through the objective lensof the optical pickup device according to the present invention;

FIG. 7 is a magnified view of portion A in FIG. 6.

DETAILED DESCRIPTION OF THE INVENTION

According to an optical pickup device of the present invention, toprevent the generation of spherical aberration from light of anintermediate area when information is reproduced from a thick disk, suchthat the intermediate area is located between a near area and a far arearelative to a central optical axis, the curvature of an intermediateregion corresponding to the intermediate area of the light is optimizedwith respect to the thick disk. Also, the light receiving area of aphoto detector is limited so that light of the far axis area cannot bereached thereto when information is reproduced from the thick disk.

Here, the near axis area represents an area around a central axis of thelens with negligible aberration. Also, the far axis area represents anarea relatively far from the optical axis compared with that of the nearaxis area, and the intermediate area represents an area between the nearand far axis areas.

FIG. 3 is a schematic diagram of an optical pickup device according tothe present invention. Like a general optical pickup device, anobjective lens 20, a beam splitter (separation unit) 60 and a detectinglens 40 are disposed in sequence on an optical path between a disk 30and a photo detector 90, and a light source 80 is located on anotheroptical path from the beam splitter 60. The disk 30 may either be a thin(digital video) disk 30a or a thick (compact) disk 30b.

In the optical pickup device having the above structure according to thepresent invention, FIGS. 4 and 5 show perspective and front views of theobjective lens 20, respectively. The reference WD_(D) denotes thedistance between the objective lens 20 and the thin disk 30a, and WD_(C)denotes the distance between the objective lens 20 and the thick disk30b. That is, in a reading or writing operation, the working distancefor the thin disk 30a is larger than that for the thick disk 30b.

The objective lens 20 has a doughnut- or ring-shaped intermediate regionA2 on at least one side, having an outer diameter which is less than thetotal significant light passing area diameter. Also, a central region A1and a periphery region A3 are placed inside and outside of theintermediate region A2, respectively. Here, the curvatures of thecentral and peripheral regions A1 and A3 are optimized for a thindigital video disk (DVD), and that of the intermediate region A2 isoptimized for a thick compact disk (CD). Also, depending oncircumstances, the intermediate region A2 may be divided into aplurality of subregions. Preferably, the photo detector 90 is designedfor only receiving light passed through the central and intermediateregions A1 and A2 of the objective lens 20 when information isreproduced from the thick disk, in which light of the far axis area isnot detected by the photo detector 90. The central region A1 is acircular region, the intermediate region A2 is a first disk-shapedregion and the periphery region A3 is a second disk-shaped region.

Thus, as shown in FIGS. 6 and 7, when information is reproduced from thethick CD 30b, only light inside the dashed line is focused on the thickCD 30b. Here, since light of the near axis area passes through theobjective lens, less spherical aberration is generated, even though thecurvature of the central region A1 corresponding to the near axis areais optimized for the thin DVD 30a. Also, when reproducing informationfrom the thin DVD 30a, light passes through the central and peripheralregions A1 and A3 whose curvature is optimized for the thin disk,thereby forming a focus on a surface including information of the thindisk 30a.

When a numerical aperture (NA) of the regions corresponding to the nearand intermediate axis areas is less than 0.4, a small focus can beformed on the thick disk, wherein the small focus is optimized for theCD disk. According to experimentation, it is preferable that the widthof the ring-shaped intermediate region is greater than 50 μm from thethin disk for a stable reproducing characteristic. Also, the data of theobjective lens for each region which is optimized for the CD and DVD aresummarized in Tables 1 and 2, respectively.

Table 1 shows lens data at the intermediate region which is optimizedfor a thick disc (CD), and Table 2 shows lens data at the central andperiphery regions optimized for a thin disc (DVD) . In these tables, thereferences to "front," "back," and "disk" represent the front surface ofthe lens, the back surface of the lens and the surface of the disk,respectively. That is, in Table 1, the data for the curved surfaces"front," "back," and "disk" refer to the data of the front surface ofthe lens at the intermediate region, the back surface of the lens at theintermediate region, and the surface of the thick disk, respectively,and in Table 2, the data for the curved surfaces "front," "back," and"disk" refer to the data of the front surface of the lens at the centraland periphery regions, the back surface of the lens at the central andperiphery regions, and the surface of the thin disk, respectively.

As described above, according to the optical pickup device of thepresent invention, the thick CD and the thin DVD can be compatiblyadopted and a signal can be detected without picking up noise regardlessof the thickness of the disk. Also, the objective lens can bemanufactured easily by a general compression or injection molding,thereby reducing manufacturing costs.

                  TABLE 1    ______________________________________    Data at the intermediate region of the objective lens.    Curved                    Refractive                                     Aspherical    Surface           Curvature                    Thickness Index  Coefficient    ______________________________________    front   2.40632 2.600000  1.505  K = 0.00000                                     A = -3.51258E-03                                     B = -6.19938E-04                                     C = -2.32191E-04                                     D = 0.00000    back   -5.11700 1.563295  1.580  K = -24.72000                                     A = 4.46350E-03                                     B = -3.69750E-03                                     C = 8.23880E-04                                     D = -7.45950E-05    disk   ∞  1.200000  1.550  Not Applicable    ______________________________________

                  TABLE 2    ______________________________________    Data at the central and periphery regions    Curved                    Refractive                                     Aspherical    Surface           Curvature                    Thickness Index  Coefficient    ______________________________________    front   2.09200 2.600000  1.505  K = -0.872110                                     A = 4.79500E-03                                     B = 6.25260E-05                                     C = 1.24380E-05                                     D = -1.76880E-04    back   -5.11700 1.563295         K = -24.72000                                     IC: Yes                                     CUF =0.000000                                     A = 4.46350E-03                                     B = -3.69750E-03                                     C = 8.23880E-04                                     D = -7.45950E-05    disk   ∞  0.600000  1.550  Not Applicable    ______________________________________

What is claimed is:
 1. An optical pickup device in an optical device andcompatible with disks having different thicknesses comprising:a lightsource; an objective lens, facing one of the disks which is placed inthe optical device, having a light passing region divided into central,intermediate and periphery regions respectively corresponding to a nearaxis area, an intermediate axis area and a far axis area of incidentlight, wherein curvatures of the central and periphery regions areoptimized for the one disk if the one disk has a first thickness and acurvature of the intermediate region is optimized for the one disk ifthe one disk has a second thickness greater than the first thickness; aphoto detector for detecting light reflected from the one disk; a beamsplitter, disposed between said objective lens and said light source,for transmitting/reflecting light from said light source toward saidobjective lens and for reflecting/transmitting light reflected from theone disk toward said photo detector.
 2. The optical pickup device asclaimed in claim 1, wherein said photo detector receives the reflectedlight only in the near and intermediate axis areas for reproducinginformation if the one disk has the second thickness.
 3. The opticalpickup device as claimed in claim 1, wherein the intermediate region ofsaid objective lens is in a ring shape.
 4. The optical pickup device asclaimed in claim 1, wherein the intermediate region is formed in atleast one side of said objective lens.
 5. The optical pickup device asclaimed in claim 1, wherein the one disk having the first thickness is adigital video disk and the one disk having the second thickness is acompact disk.
 6. An optical pickup in an optical device and compatiblewith disks of different thicknesses, wherein the optical pickupreproduces from or records information to one of the disks which isloaded in the optical device, the optical pickup comprising:a lightsource to emit an incident light; an objective lens having an opticalaxis and a light passing region divided into central, intermediate andperiphery regions relative to the optical axis, wherein curvatures ofthe central and periphery regions are optimized for the one disk if theone disk has a first thickness and a curvature of the intermediateregion is optimized for the one disk if the one disk has a secondthickness greater than the first thickness; a photo detector to detectlight reflected from the one disk and transmitted through said objectivelens; and a separation unit to separate the incident light transmittedfrom said light source from the reflected light reflected by the onedisk.
 7. The optical pickup as claimed in claim 6, wherein:the centralregion has a circular cross-section centered about the optical axis; theintermediate region has a disk-shaped cross-section adjacent to andextending from an outer diameter of the central region; and theperiphery region has a disk-shaped cross-section adjacent to at andextending from an outer diameter of the intermediate region.
 8. Theoptical pickup as claimed in claim 6, wherein the photo detector onlyreceives reflected light passing through the central and intermediateregions if the one disk has the second thickness.
 9. The optical pickupas claimed in claim 7, wherein the photo detector only receivesreflected light passing through the central and intermediate regions ifthe one disk has the second thickness.
 10. The optical pickup as claimedin claim 6, wherein the central and intermediate regions have anumerical aperture less than approximately 0.4.
 11. The optical pickupas claimed in claim 9, wherein the central and intermediate regions havea numerical aperture less than approximately 0.4.
 12. The optical pickupas claimed in claim 7, wherein the disk-shaped intermediate region isgreater than 50 μm from the one disk if the one disk has the firstthickness.
 13. An optical pickup in an optical device and compatiblewith disks of different thicknesses, wherein the optical pickupreproduces from or records information to one of the disks which isloaded in the optical device, the optical pickup comprising:a lightsource to emit an incident light; an objective lens having an opticalaxis and a curved light passing portion with at least one first regionhaving a first curvature optimized for the one disk if the one disk hasthe first thickness and a second region having a second curvatureoptimized for the one disk if the one disk has the second thickness; aphoto detector to detect light reflected from the one disk andtransmitted through said objective lens; and a separation unit toseparate the incident light transmitted from said light source from thereflected light reflected by the one disk.
 14. The optical pickup asclaimed in claim 13, wherein:the at least one first region has acircular region extending from the optical axis to a first diameter, thesecond region being a first disk-shaped region extending from the firstdiameter to a second diameter, and the at least one region furtherhaving a second disk-shaped region and extending from the seconddiameter to a third diameter.
 15. The optical pickup as claimed in claim14, wherein said photo detector receives the reflected light only in thecircular and first disk-shaped regions if the one disk has the secondthickness.
 16. The optical pickup as claimed in claim 14, wherein thecircular and first disk-shaped regions have a numerical aperture lessthan approximately 0.4.
 17. The optical pickup as claimed in claim 15,wherein the curved light passing portion faces away from the one disk.18. The optical pickup as claimed in claim 7, wherein the firstdisk-shaped region is greater than 50 μm from the one disk if the onedisk has the first thickness.
 19. An optical pickup device for anoptical device compatible with different types of optical memory media,said optical pickup device comprising:a light source; an objective lensto transmit light emitted from said light source onto one of saidoptical memory media, said objective lens having a plurality of lensportions having different optical characteristics, wherein one of saidplurality of lens portions focuses said light onto said one opticalmemory medium regardless of the type of said one optical memory medium;a photodetector to detect light reflected from said one optical memorymedium; and beam splitting means to receive said light emitted from saidlight source for transmission to said objective lens and for receivingsaid light reflected from said one optical memory medium fortransmission to said photodetector.
 20. The optical pickup device asclaimed in claim 19, wherein said one optical memory medium is a compactdisk or a digital video disk.
 21. The optical pickup device as claimedin claim 19, wherein said objective lens has a discontinuous curvedsurface.
 22. The optical device as claimed in claim 19, wherein saidplurality of lens portions of said objective lens are integrally formed.23. The optical pickup device as claimed in claim 19, wherein saidplurality of lens portions comprises:a first portion to focus said lightemitted from said light source onto said one optical memory mediumregardless of a thickness of said one optical memory medium; a secondportion to focus said light emitted from said light source onto said oneoptical memory medium if said optical memory medium has a firstpredetermined thickness; and a third portion to focus said light emittedfrom said light source onto said one optical memory medium if saidoptical memory medium has a second predetermined thickness which isdifferent from said first predetermined thickness.
 24. The opticalpickup device as claimed in claim 23, wherein only said light passingthrough said first portion and said second portion are focused onto saidoptical memory medium if said one optical memory medium has said firstpredetermined thickness, and only said light passing through said firstportion and said third portion are focused onto said optical memorymedium if said one optical memory medium has said second predeterminedthickness.
 25. The optical pickup device as claimed in claim 23, whereinsaid first predetermined thickness is greater than said secondpredetermined thickness.
 26. The optical pickup device as claimed inclaim 23, wherein said first portion is disposed at a center part ofsaid objective lens including a center point, said second portion isdisposed adjacent to said first portion and said third portion isdisposed adjacent to said second portion at an outer periphery of saidobjective lens.
 27. The optical pickup device as claimed in claim 26,wherein said first portion is formed to be substantially disk shaped,said second portion is formed to be substantially disk ring shapedsurrounding said first portion and said third portion is formed to besubstantially ring shaped surrounding said second portion.
 28. Theoptical pickup device as claimed in claim 23, wherein said opticalcharacteristics of said first portion and said third portion are thesame, and said optical characteristics of said second portion aredifferent from that of said first portion and said third portion. 29.The optical pickup device as claimed in claim 28, wherein said opticalcharacteristics include curvatures, said curvature of said secondportion being different from said curvature of said first portion andsaid third portion.
 30. The optical pickup device as claimed in claim23, wherein said second portion has a cutout portion on a surfacethereof.
 31. The optical pickup device as claimed in claim 29, whereinsaid second portion has a cutout portion on a surface thereof.
 32. Theoptical pickup device as claimed in claim 23, wherein said first portionand said second portion have a numerical aperture of less thanapproximately 0.4.
 33. The optical pickup device as claimed in claim 23,wherein said photodetector receives only said reflected light from saidone optical memory medium originally transmitted to said one opticalmemory medium by said first and second portions of said objective lenswhen said one optical memory medium has said first predeterminedthickness.
 34. The optical pickup device as claimed in claim 32, whereinsaid photodetector receives only said reflected light from said oneoptical memory medium originally transmitted to said optical memorymedium by said first and second portions of said objective lens whensaid one optical memory medium has said first predetermined thickness.35. The optical pickup device as claimed in claim 23, wherein a distanceof the objective lens from a surface of said one optical memory mediumvaries in accordance with a thickness of said one optical memory medium.36. The optical pickup device as claimed in claim 35, wherein saiddistance is a first predetermined distance when said one optical memorymedium has said first predetermined thickness and said distance is asecond predetermined thickness when said one optical memory medium hassaid second predetermined thickness, said first predetermined distancebeing smaller than said second predetermined distance.
 37. The opticalpickup device as claimed in claim 30, wherein said one optical memorymedium is a compact disk or a digital video disk.
 38. The optical pickupdevice as claimed in claim 31, wherein said one optical memory medium isa compact disk or a digital video disk.
 39. An objective lens for use inan optical device compatible with different types of optical memorymedia, said objective lens having a plurality of portions havingdifferent optical characteristics, wherein one of said plurality of lensportions focuses light onto one of said optical memory media independentof the type of said one optical memory medium.
 40. The objective lens asclaimed in claim 39, wherein said optical memory medium is a compactdisk or a digital video disk.
 41. The objective lens as claimed in claim39, wherein said objective lens has a discontinuous curved surface. 42.The objective lens as claimed in claim 39, wherein said plurality ofportions of said objective lens are integrally formed.
 43. The objectivelens as claimed in claim 39, wherein said plurality of lens portionscomprises:a first portion to focus a light emitted from a light sourceonto said one optical memory medium independent of a thickness of saidone optical memory medium; a second portion to focus said light emittedfrom the light source onto said one optical memory medium if saidoptical memory medium has a first predetermined thickness; a thirdportion to focus said light emitted from said light source onto said oneoptical memory medium if said optical memory medium has a secondpredetermined thickness which is different from said first predeterminedthickness.
 44. The objective lens as claimed in claim 43, wherein saidobjective lens only focuses the light passing through said first portionand said second portion onto said optical memory medium if said oneoptical memory medium has said second predetermined thickness.
 45. Theobjective lens as claimed in claim 43, wherein said first predeterminedthickness is greater than said second predetermined thickness.
 46. Theobjective lens as claimed in claim 43, wherein said first portion isdisposed at a center part of said objective lens including a centerpoint, said second portion is disposed adjacent to said first portionand said third portion is disposed adjacent to said second portion at anouter periphery of said objective lens.
 47. The objective lens asclaimed in claim 43, wherein said first portion is formed to besubstantially disk shaped, said second portion is formed to besubstantially ring shaped surrounding said first portion and said thirdportion is formed to be substantially ring shaped surrounding saidsecond portion.
 48. The objective lens as claimed in claim 43, whereinsaid optical characteristics of said first portion and said thirdportion are the same and said optical characteristics of said secondportion are different from that of said first portion and said thirdportion.
 49. The objective lens as claimed in claim 48, wherein saidlens optical characteristics include curvatures, said curvature of saidsecond portion being different from said curvature of said first portionand said third portion.
 50. The objective lens as claimed in claim 43,wherein said second portion has a cutout portion on a surface thereof.51. The objective lens as claimed in claim 49, wherein said secondportion has a cutout portion on a surface thereof.
 52. The objectivelens as claimed in claim 43, wherein said first portion and said secondportion have a numerical aperture of less than approximately 0.4. 53.The objective lens as claimed in claim 50, wherein said optical memorymedium is a compact disk or a digital video disk.
 54. A method offocusing a light source onto an optical memory medium in an opticaldevice compatible with different types of optical memory media, saidmethod comprising the steps of:receiving light from a light emittingsource; focusing a first portion of said light onto said optical memorymedium independent of a type of said optical memory medium; focusing asecond portion of said light onto said optical memory medium if saidoptical memory medium is a first predetermined type; and focusing athird portion of said light onto said optical memory medium if saidoptical memory medium is a second predetermined type.
 55. The method asclaimed in claim 54, wherein only said first and second portions of saidlight are focused onto said optical memory medium if said optical memorymedium is said first predetermined type and only said first and thirdportions of said light are focused onto said optical memory medium ifsaid optical memory medium is said second predetermined type.
 56. Themethod as claimed in claim 54, wherein a thickness of said firstpredetermined type is greater than a thickness of said secondpredetermined type.
 57. The method as claimed in claim 55, wherein saidfirst predetermined type is a compact disk and said second predeterminedtype is a digital video disk.
 58. The optical pickup as claimed in claim8, wherein the photo detector only receives reflected light passingthrough the central and periphery regions if the one disk has the firstthickness.
 59. The optical pickup as claimed in claim 9, wherein thephoto detector only receives reflected light passing through the centraland periphery regions if the one disk has the first thickness.